Co-continuous morphology development in partially miscible PMMA/PC blends

Poly(methyl methacrylate) (PMMA)/polycarbonate (PC) partially miscible blends were produced via melt blending in an internal mixer over the entire range of composition at two different viscosity ratios. The morphology of this low interfacial tension system was investigated by scanning electron microscopy, solvent extraction/gravimetry and surface area measurement (BET) after selective extraction. The partial miscibility of these blends was evaluated by T g measurements from dynamic mechanical thermal analysis. The co-continuous morphology development curve obtained from gravimetry is commonly reported in the literature as the %continuity vs. the vol% fraction of the dispersed phase for fully phase separated systems. Such systems possess pure phases of A and B. Partially miscible blends on the other hand demonstrate immiscibility between an A-rich phase and a B-rich phase. Quantitative estimation of the partial composition of the minor components in each respective rich phase was calculated using the Fox equation. Using this data, an approach to correcting the gravimetry results to take into account the partial miscibility of the PMMA/PC system is proposed. The co-continuous morphology development curve is then presented as the %continuity vs. the vol% fraction of the PMMA-rich phase. This corrected curve demonstrates the features of a highly interacting polymer blend: a low percolation threshold and a broad co-continuity region. The BET technique shows that the pore size of the extracted co-continuous blends is dependent on composition, the pore diameter increases with total PMMA content. Use of a low molecular weight PC shifts the co-continuous morphology development curve to higher volume fraction values of PMMA-rich phase. It is suggested that this is the result of a lower dispersed phase thread stability due to the lower matrix viscosity.